glsl: Fix copying function's out to temp if dereferenced by array

glsl: Fix copying function's out to temp if dereferenced by array

Function's out variable could be an array dereferenced by an array:
 func(v[w[i]]);
or something more complicated.

Copy index in any case.

Fixes: 76c27e47b906 ("glsl: Copy function out to temp if we don't directly ref a variable")
Signed-off-by: Danylo Piliaiev <danylo.piliaiev@globallogic.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>